Generally speaking, the present invention relates to refrigeration mechanisms such as those usually found in refrigerators and the like and more specifically to refrigeration mechanisms which include a refrigerant; a means for pressurizing the refrigerant, a means for liquifying the refrigerant, a means for vaporizing the refrigerant; and a means for circulating air to be refrigerated wherein the improvement comprises a means for sensing actual frost accumulation within the refrigeration mechanism.
In most "frost-free" refrigerators the time at which the defrost mechanism turns-on is either preselected or a function of the temperature within the refrigeration compartment and accordingly it in fact does not operate as a direct function of the actual accumulation of frost within the refrigeration mechanism itself. Accordingly, in many instances defrost mechanisms function more frequently than is necessary to maintain substantially "frost-free" conditions in a refrigeration compartment thereby resulting in the inefficient utilization of power.
Relying upon the principle that the dielectric constant of ice is considerably greater than that of air the present invention provides a means for sensing frost accumulation within a refrigeration mechanism which employs a capacitance sensitive element. The above stated principle and its application to the detection of the presence of ice is not new e.g. see Hoenisch et al Patent issued Jan. 2, 1968 (U.S. Pat. No. 3,360,951) and Dow Patent issued July 24, 1962 (U.S. Pat. No. 3,046,537). However, the present invention applies the principle to the sensing of frost accumulation in a refrigeration mechanisms. One of the primary difficulties in employing a capacitance sensitive element in an environment where ice or frost is allowed to actually accumulate on the electrodes of such element is the deformation of the electrodes. This deformation results from the contraction and expansion associated with the freezing and melting processes. Naturally, as the electrodes are deformed the capacitance value of the capacitance sensitive element will vary resulting in a capacitance sensitive element which senses unpredictable amounts of accumulated frost.